1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium in which color images are formed and erased reversibly based on color-developing reactions between an electron-donating coloring compound and an electron-accepting compound by controlling applied thermal energies, and also relates to a reversible thermosensitive recording label, a reversible thermosensitive recording member, an image-processing apparatus and a method which employ the reversible thermosensitive recording medium respectively.
2. Description of the Related Art
Thermosensitive recording media which utilize reactions between an electron-donating coloring compound (hereinafter, sometimes referred as “coloring agent” or “leuco dye”) and an electron-accepting compound (hereinafter, sometimes referred as “color developer”) have been well-known, and have been broadly utilized as output papers of facsimiles, word processors and scientific instrumentation apparatuses, with an advance of office automation, and nowadays in magnetic thermosensitive cards such as a pre-paid card and point card. However, there is still the need for the development of reversible thermosensitive recording media which are repeatedly rewritable in view of an environmental issue and a recycling of the resource.
As such the reversible thermosensitive recording media, there has been proposed a reversible thermosensitive recording medium which, by combining a color developer of an organic phosphoric acid compound, aliphatic carbonic acid compound or phenol compound containing a long chain aliphatic hydrocarbon group, and a coloring agent of leuco dye, easily realizes coloring and decoloring by controlling heating and cooling conditions, is enables to stably maintain the coloring state and the decoloring state at room temperature, and is able to repeatedly perform coloring and decoloring (see Japanese Patent (JP-B) No. 2981558). After this technique was proposed, there was proposed a specific molecular structure of the phenol compound having a long chain aliphatic hydrocarbon group (see JP-B Nos. 3380277, and 3557076). Among the compounds having these proposed structures, it has been known that a urea derivative having a phenol group and a long chain alkyl group shows particularly excellent erasing ability.
When a thermosensitive recording medium using such the urea derivative as a color developer is repeatedly rewritten by a printer, there are however defects such that an amount of dusts adhered to a heat source, e.g. a thermal head or a ceramic heater, tends to be increased, and a density of color image is therefore decreased due to the deposition of the dusts. Since an applied energy from the heat source is increased as a transfer speed of the printer is increased, the adhesion of the dusts is prone to be increased. As a result, print failures, i.e. lower density, friction mark, white out and the like, are caused, and such the print failures become a large problem when realizing a high speed printer.
As a method for preventing dusts adhesions to a heat source such as a thermal head, there has been proposed a method wherein a protective layer containing a electron beam curing resin and filler is arranged in a thermosensitive recording medium (see Japanese Patent Application Laid-Open (JP-A) Nos. 2000-25336, and 11-240251). According to this method, the protective layer however becomes a barrier for transferring a heat from a thermal head to a thermosensitive recording layer, and thus coloring and decoloring sensitivity is lowered. This problem becomes significant especially when a transfer speed of a printer is set at high speed. In addition, there have been proposed a method wherein a silicone resin is added to a protective layer (see JP-A No. 2005-53124), a method wherein a surface roughness of a protective layer is controlled at a certain condition (see JP-A No. 2002-166649), and a method wherein a barrier layer containing an organic substance is disposed (see JP-A No. 09-267568). In these methods, there is also a problem that the coloring and decoloring sensitivity is lowered. Therefore, these methods are also not yet effective.
JP-A Nos. 08-45038 and 07-164648 propose a method for removing dusts on a thermal head by using a cleaning member. JP-A No. 06-199041 proposes a method in which a liquid is applied on a thermal head. However, these proposed methods need to be performed additionally apart from a coloring and decoloring process of a reversible thermosensitive recording medium, and thus they require more processes and the productivity is lowered.
JP-A No. 05-124346 proposes a method in which an undercoat layer is disposed in a reversible thermosensitive recording medium, and as the undercoat layer, it uses a cushion member formed by coating polyurethane foam or foamable plastic filler, and heating for foaming. However, this method requires an operation of heating for foaming after applying the foamable plastic filler. Therefore, the operation in the production process becomes complicated, and the particle size distribution of the foamed particles becomes broad after heating. As a result, there are problems such that a surface smoothness is decreased due to coarse foamed particles, and cushioning properties are lowered since some particles are remained without being completely formed.
JP-B No. 3565564 proposes to dispose an undercoat layer containing thermosensitive gelling latex and fine hollow particles. In this method, it is very difficult to control the conditions for applying the thermosensitive gelling agent, and thus this method is not suitable for the mass production.
Accordingly, there is still a need for providing a reversible thermosensitive recording material which decreases an amount of dusts adhesion to a heat source such as a thermal head, and has excellent erasing ability in high transfer speed.